score = eval(input("请输入成绩分数："))
if 60 <= score:
    print("成绩已合格")
    if 90 <=score <= 100:
        print("成绩很好")


a=50
if a>20:
    print("变量a大于20")
else:
    print("变量a不大于20")



score=eval(input("请输入成绩分数"))
if score>=60:
    print("成绩及格")
    if score>=90:
        print("成绩很好")
    else:
       print("成绩一般")



score=eval(input("请输入成绩分数"))
if score>=60:
    print("成绩及格")
    if score>=90:
        print("成绩很好")
    else:
        print("成绩一般")
else:
    print( "成绩不及格")
    if score<30:
        print("成绩极差")
    else:
        print("成绩较差")



score=eval(input("请输入一个成绩分数"))
if score>= 90:
    print("成绩优秀")
elif score >= 80:
    print("成绩良好")
elif score >= 70:
    print("成绩中等")
elif score >= 60:
    print("成绩较好")
else:
    print("成绩不及格")

def shi(举头望明月):
    print('举头望明月，低头思故乡')
    shi()

def add():
    a = 3
    b = 5
    s = a + b
    print(s)
    return a